1. Field of the Invention
The present invention relates to a liquid-crystal projection device i.e. what is known as a projector and in particular relates to improvements in the light source and peripheral optical system of a small-size liquid-crystal projection device.
2. Description of the Related Art
As the light sources employed is conventional liquid-crystal projection devices, light sources using a fluorescent tube or light-guide plate or electrical discharge-type light sources such as metal halide lamps have come to be employed.
In particular, Japanese Patent Laid-Open number Sho. 51-119243 discloses a flat plate-shaped light source. This specification states that the flat plate-shaped light source employs electroluminescence i.e. electroluminescent elements.
However, in the case of a light source employing a fluorescent tube or light-guide plate, it is difficult to make the diameter of the fluorescent tube etc. small. There was therefore the problem that miniaturization of a liquid-crystal projection device was difficult, since the thickness of the light source itself could not be reduced below the diameter of the fluorescent tube.
Also, in the case of an electric discharge-type light source such as a metal halide lamp, the reflector of large aperture that was considered necessary to direct the light diverging from the light source parallel to the liquid crystal panel was a factor impeding miniaturization of the liquid-crystal projection device.
In particular in the case of a liquid-crystal projection device for color display, further miniaturization the liquid-crystal projection device was difficult owing to the need to provide liquid crystal display elements consisting of a light source as aforementioned and liquid crystal panel for each of the primary colors constituting the color image.
Also, Japanese Patent Laid-Open number Sho. 51-119243 does not clearly disclose a material constituting a luminescent layer of an electroluminescent element. When the conventional inorganic electroluminescent material is employed as material for this luminescent layer, light from the electroluminescent element is light of a highly divergent character. This therefore suffered from the problem that projection of a bright image could not be achieved since the light could not be effectively directed into the aperture of the projection lens.
A further problem was that the drive voltage required for an electroluminescent element using inorganic material is at least 100 volts, which is comparatively high.